Coiler for very thin metal strip

ABSTRACT

To enable safe coiling of very thin metals at high speed, the invention discloses a coiler comprising a mandrel of considerably smaller diameter then prior art mandrels, enabling said mandrel to be directly driven by an electric motor without using reduction gears. The coil outer diameter is also reduced, the result being a coiler having far lower polar moment of inertia than prior art coilers, therefore greatly reducing the incidence of tension errors and strip breaks. The mandrel is constructed specifically for operation with a spool upon which the coil is wound, and incorporates the novel feature of concentric expansion using a plurality of circumferentially oriented wedges, which ensures uniform support and grip of the spool bore, holding said spool and coil concentric with the axis of the mandrel.

BACKGROUND OF THE INVENTION

Prior art coilers, used for many years for coiling metal strip in coldrolling mill installations can generally be divided into twotypes—firstly, those having collapsible mandrels, and secondly, thosehaving non-collapsible mandrels also known as solid block mandrels.These types are well known in the art. Collapsible block mandrels aredesigned to operate in the expanded position, where the outside diameteris fixed at a value which is somewhere in the range 400 mm (small,narrow rolling mill installations) up to 750 mm (large, wide rollingmill installations), the most common diameters being 508 mm (20 in.) and610 mm (24 in.). After completion of rolling, the mandrel is collapsedto a smaller diameter, enabling the coil to be stripped, that is removedfrom the mandrel by transferring it in an axial direction until itclears the mandrel. The mandrel typically consists of internal pyramidshaft 61, said shaft being keyed to segments 63, which form the outsidecylindrical shape of the mandrel. As is shown in FIG. 1, the mandrel istypically expanded and collapsed by axially shifting said pyramid shaftrelative to said segments 63 using a hydraulic rotating cylinder 64,mounted at the back end of the mandrel drive shaft. For narrow strip themandrel is cantilevered out from a drive shaft, but for wider strip, athird bearing, known as the outboard bearing 62 is used to support themandrel at its front end during coiling. The support structure for theoutboard bearing can be retracted to enable the coil to be stripped whencoiling is complete.

When thin gauge strip (less than about 0.5 mm thick) is to be coiled ona collapsible mandrel, it is essential to use a spool (a hollow cylinderusually made of steel) inside the coil to avoid damaging the inside ofthe coil. The spool inside diameter must be just less than the expandeddiameter of the mandrel so that the mandrel will grip the spool when themandrel is expanded. Then the coil is wound on the outside of the spool.Eventually, at a subsequent process such as annealing or slitting, thecoil must be unwound from the spool, enabling the spool to be returnedto the rolling mill installation for use with another coil.

Solid block mandrels, as the name implies, are made from a solid blockof alloy steel. They consist of a cylindrical body with an integralreduced diameter portion (a neck portion) at each end, upon which radialbearings are mounted. At the outer end of each neck piece a halfcoupling is fixed. A grooved wheel is mounted on the outside of eachradial bearing.

In the working position of the coiler, the wheels are clamped inposition upon a base and a sliding coupling is used to connect themandrel to a drive shaft. The drive shaft is mounted on two radialbearings, similarly to the drive shaft of the collapsible bearingmandrel. Solid block body diameter range is similar to that forcollapsible mandrels.

Spools are never needed with solid blocks—even very thin strip can becoiled on a solid block. However, after coiling it's necessary to rewindthe strip from the solid block to a collapsible mandrel, since rewindingis the only way to remove a coil from a solid block. Usually a millinstallation having solid block coilers will include equipment forrewinding the coils, at low tension, to a collapsible rewinder mandrel,using a light spool at the rewinder in the case of thin strip.

In virtually all cases, the drive to mandrel of both solid andcollapsible varieties is via a variable speed electric motor 65,traditionally D.C., but more commonly A.C. today, and through reductiongears 66, the drive shaft described above being the output shaft of thereduction gear box, the input shaft 67 of said gear box being directlycoupled to the drive motor through drive spindle 68. The reductiongears, usually having a ratio of 3:1 or more, are needed to achieve therequired coiling speeds and torques using a motor having standard speedrange.

In general, high strength materials such as stainless steels cannot berolled to a strip thickness less than around 25 microns (0.001″) unlessa very small Sendzimir mill having work rolls less than 25 mm indiameter is used. Such mills only exist in widths of around 250 mm orless. Because such materials must be rolled with very high tensionsapplied to the strip, extremely high compressive stresses are developedin the mandrel around which the strip is coiled, and the preferredsolution is a solid block mandrel, which is best able to withstand suchstresses. The strip subsequently has to be rewound at low tensions toremove it from the solid block mandrel.

For coiling softer materials such as aluminum and copper at very thingauges, it's possible to use collapsible mandrels using spools. As thestrip tensions used when coiling these materials are relatively low,then spools made from plain carbon steel, relatively thin walled and sorelatively inexpensive, are able to withstand the compressive forcesapplied by the coil as it is wound on the spool. The spools can even beused for shipping the coils so rewinding can be avoided in many cases.These materials can be rolled down to foil gauges of 25 micron and lessusing larger work rolls of 50 mm in diameter or more and so can berolled on many standard Sendzimir mills at widths up to about 750 mm.

The problem when rolling softer materials at very light gauges of 150microns and below, is that the strip tension when coiling must bemaintained at a very steady low value at all times yet the tensionstress in the strip must be quite high to achieve good strip flatnessand to get the desired reductions. This includes (a) during speed-up andslow-down of the mill at the ends of the coil and (b) during operationof the mill screwdown to adjust the thickness or elongation of the stripin the mill. The very light gauge strip is very fragile and prone tobreak if the tension is not held steady. Using the prior art coilerdesigns described above, there are several factors which can induceunacceptable tension fluctuations, and thus cause the strip to break.

-   -   1. The high polar moment of inertia of all the rotating parts        includes mandrel, drive shaft, rotating cylinder, driven gear,        drive gear, input shaft, input coupling and drive motor        armature. This inertia can give rise to large tension        fluctuation as the speed changes. Note that the polar moment of        inertia of the latter four items must be multiplied by the        square of the gear ratio to find their equivalent values at the        mandrel.    -   2. Because the mandrel is not perfectly round, and/or if the        spool is not perfectly cylindrical, or there is some variation        in spool wall thickness, some cyclic variation in strip speed        will occur, and the resultant tension variation will be        proportional to the inertia of the rotating parts.    -   3. Because the total weight of the rotating parts is high, even        when using anti-friction bearings the friction in the bearings        will cause significant tension errors in the strip.    -   4. Because of large sizes and large number of rotating elements,        there will be strip tension errors due to windage, which will        vary with the speed of rotation, and will therefore vary with        both coiling speed (m/s or ft/sec) and coil diameter.

OBJECT OF THE INVENTION

The object of the invention is to achieve a coiler design for very thingauge metal strip which overcomes the drawbacks of prior art systems by(a) greatly reducing the polar moment of inertia of the rotatingmembers, (b) gives a collapsible mandrel designed for operation withspools, which maintains a true circle outer diameter throughout theexpand/collapse range in order to ensure concentricity of coil, spooland mandrel and (c) provides for measurement of strip tension withoutthe use of pass line rollers. These improvements minimize strip tensionvariation during coiling, and thus enable coiling at higher speeds withreduced risk of strip breaks.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1: shows a prior art mandrel, gear reducer and drive motor in planview, drawn with front end of the mandrel at the left side.

FIG. 2: shows one embodiment of a coiler consisting a mandrel, driveshaft and drive motor in plan view, according to the present invention,drawn with front end of the mandrel at the left side.

FIG. 3: shows partial side elevation and section of a mandrel accordingto the present invention, drawn with front end of the mandrel at theleft side, and the back end of the mandrel at the right side.

FIG. 4: shows a partial end elevation section of a mandrel as viewedfrom the line 4-4 of FIG. 3.

FIG. 5: shows some scrap sections taken from FIG. 4.

FIG. 6: shows an enlarged view of the stave return spring assembly inFIG. 3.

FIG. 7: shows a longitudinal section of a mandrel according to thepresent invention, drawn with front end of the mandrel at the left side,and the back end of the mandrel at the right side.

FIG. 8: shows a transverse section of a mandrel according to the presentinvention.

FIG. 9: shows a longitudinal view of mandrel shaft, oil feed ring andaxial retention ring and outboard support bearing of a mandrel accordingto the present invention, drawn with front end of the mandrel at theleft side, and the back end of the mandrel at the right side.

FIG. 10: shows a view taken from the rear of the mandrel, showing therear axial retention structure.

FIG. 11: shows a transverse section of a mandrel at the front end plate,with the mandrel in a partially expanded condition, gripping the insidediameter of a spool.

FIG. 12: shows a transverse section of a mandrel at the front end platewith the mandrel fully expanded.

FIG. 13: shows a transverse section of a mandrel at the front end plate,with the mandrel fully collapsed.

FIG. 14: shows a radial cross section of a mandrel having linear wedgesurfaces replaced by curved wedge surfaces to give improved operationand extended life.

DETAILED DESCRIPTION OF THE INVENTION

Because this coiler is designed for very light gauges in relatively softmaterials only, spools 106 (FIG. 1 and FIG. 2) will always be used. Inthe embodiment shown in FIG. 2, the mandrel is designed to engage with aspool having an inside diameter of 12 in. or 305 mm. This is muchsmaller than the prior art diameter range of 508-610 mm, and thus can bedirectly driven by an electric motor having a standard speed range. Themandrel has to expand tightly against the inside of the (nominallycylindrical) spool. Depending upon the material of the spool and thetension stress applied to the strip as it is coiled, the spool outsidediameter would be in the range 330-350 mm. To avoid the need forexcessive drive torque and thus to enable a standard drive motor to beused, the maximum coil diameter is limited to around 600 mm. Even so,the lengths of light gauge coils at this diameter are sufficient toensure high productivity.

By using such small mandrel and coil outer diameters, ifs possible touse direct drive between motor and mandrel as shown in FIG. 2. Thecombination of these reduced diameters and elimination of reductiongears leads to an order of magnitude reduction in polar moment ofinertia of mandrel, coil and drive relative to the prior art. It shouldbe noted here that an outboard bearing 51 and retractable supportstructure according to the prior art may be used to support the frontend of the mandrel.

Since there is always a spool, and it's not necessary to support theinside diameter of the spool continuously around its circumference wesupport the spool only at a finite number of points. In the embodimentshown in the drawings, we support the spool by a total of 24 identicalsupport members (staves) 14, which are incorporated in the mandrel, andare equally spaced around the circumference of the mandrel,approximately 40 mm apart as seen in FIG. 4. This provides sufficientsupport for a spool 17.5 mm thick (outside diameter 340 mm). The stavesare spaced apart and guided by cage 13 in which 24 equally spaced axialslots are machined, into each of which a stave 14 is mounted. Said slotsconstrain said staves to permit only movement in a radial directionrelative to said cage. It is also possible to use fewer than 24 stavesand slots. This simplifies and strengthens the structure, but mayrequire a greater spool thickness because of the resulting increasedspacing of the staves. In no case would fewer than 8 support members(staves) be adequate.

An inner sleeve 12, mounted on and keyed to drive shaft 11 by keys 16and 17 (FIG. 7), incorporates 24 identical wedges 33, said wedges beingequally spaced around the outside circumference of said inner sleeve.These wedges, unlike the expansion wedges of all prior art mandrelswhich are oriented in the axial direction, are oriented in acircumferential direction and form the outer surface of said innersleeve. Return springs 15, one mounted in each end of cage 13, hold eachstave 14 firmly inwards against its mating wedge 33. Each of said returnsprings is secured in said cage using a special threaded retainer plug40, as seen in the enlarged view of FIG. 6.

It is envisaged that standard construction materials would be used forthe mandrel, such as steel for shaft 11, end plates 18,18 a, oil feedring 19 and axial retention ring 34, inner sleeve 12 and cage 13, andother materials such as bronze or ductile iron for the staves 14.

The expand/collapse mechanism is as follows:

As can be seen from FIG. 4, if inner sleeve 12 is rotated in acounter-clockwise circumferential direction relative to cage 13 andstaves 14, said staves will ride up wedges 33 in a radial direction andincrease the outer diameter of the mandrel, this diameter being that ofthe circle that joins or circumscribes the outer ends of the 24 staves14. This is the expansion mechanism.

Because both staves and wedges are equally spaced around the mandrelaxis, the radial movement of the staves will be synchronized such thatsaid outer diameter is always concentric with the said mandrel axis, andwill grip and support the inside diameter of said spool to hold saidspool concentric with said mandrel axis.

If inner sleeve 12 is now rotated in a clockwise circumferentialdirection relative to cage 13 and staves 14, with return springs 15holding staves 14 firmly down on wedges 33, said staves will ride downsaid wedges and reduce said outer diameter. This is the collapsemechanism.

Note that the total relative rotation of said inner sleeve relative tosaid cage and said staves, from fully collapsed to fully expandedcondition is 10 degrees.

In FIG. 4, and FIGS. 11-13, the expansion wedges are shown with astraight profile, necessitating a curved profile on the inner ends ofthe staves because the wedges are rotating relative to the staves, andthus the wedge angle relative to the staves changes as the mandrel isexpanded.

It's also possible to use a curved surface of the wedges and matchingcurvature of the inner ends of the staves, in order to improve theuniformity of pressure distribution over the contact area between eachstave and its mating wedge, as is described later in this specification.

If torque is applied in a clockwise direction to the cage and staves inthe drawings, by the application of strip tension to the coil mounted onthe spool which contacts the 24 staves, this tension torque will urgethe staves to ride up the wedges and so increase the pressure betweenstaves and spool inner bore, thus tightening the grip of the staves onthe spool. The mandrel thus has a self tightening action. Such an actionis new in the art. Since, on a coiler, the tension torque always acts inone direction, regardless of the direction of rotation (i.e. regardlesswhether the coil is being wound or unwound) this self-tightening actionis always present.

Clearly, for a reversing mill having a coiler at the left side and acoiler at the right side of the mill stand(s) in a symmetricalarrangement, the tension torque direction, either clockwise orcounter-clockwise, on the left hand coiler will be opposite from that ofthe right hand coiler. The same major components can still be used forboth coiler mandrels, because inner sleeve 12 and staves 14 will simplybe assembled back to front in one mandrel relative to the other in orderto reverse the orientation of the wedges and staves. In this way bothmandrels will be self-tightening, even though the tension torque on onemandrel always acts in a clockwise direction, and the tension torque onthe other mandrel always acts in a counter-clockwise direction, whenviewed from the front of the mandrel in each case. It follows that thecross section shown in FIG. 14 will be valid for one mandrel viewed fromthe front and for the other mandrel viewed from the back.

The arrangement shown in the embodiments of FIG. 4, FIG. 8 and FIGS.11-14 is suitable where the tension torque direction is clockwise whenviewed from the front (as is the case with these drawings). This wouldbe the left coiler, if over-winding, or the right coiler, ifunder-winding.

In fact, even though this mandrel is self-tightening, it may benecessary to provide additional force when expanding the mandrel, inorder to apply sufficient radial force to the bore of the spool by thestaves 14, so that the spool will not slip on the staves while fullstrip tension is applied to the outside of the coil. It's also necessaryto expand the mandrel until said mandrel grips the bore of the spoolinitially. The initial expansion and additional force are provided byhydraulic expand cylinders, as follows:

At both front and back ends of the mandrel, respective front end plate18 and back end plate 18 a are provided, said end plates being attachedto cage 13, one at each end of said cage, by axial cap screws 30 asshown in FIG. 3. These end plates are mounted and keyed to shaft 11 andhave the primary function of axially locating inner sleeve 12 relativeto said cage, and locating said cage concentric with shaft 11 and innersleeve 12, and also of applying additional expansion force, which theyapply by means of hydraulic pistons 21 which slide within hydraulicexpand cylinders 22 bored into said end plates and bear against lugs 20which project into recesses 28 in end plates as shown in FIGS. 11-13.Note that said hydraulic expand cylinders are enclosed by plug 41screwed into end plate 18 or 18 a, hydraulic oil being supplied throughfeed holes 23, 24, 25, 26 at the front, and feed holes 38, 37 and 26 atthe back, as shown in FIG. 7. When pressure is applied to said hydraulicexpand cylinders, pistons 21 press against lugs 20, which are formed ateach end of inner sleeve 12 (two lugs at each end) in order to rotatesaid inner sleeve relative to said end plates and cage 13. This causesthe staves 14 to ride up the wedges on inner sleeve 12 and thus expandthe mandrel and push the staves tightly against the bore of the spool onwhich the coil is to be wound, as shown in FIG. 11.

Return springs 29 acting through plungers 39, in line with saidhydraulic expand cylinders, serve to collapse the mandrel and to retractsaid pistons prior to stripping the coil. This they do by pressing saidplungers against lugs 20 thus rotating the inner sleeve to collapse themandrel when pressure is released from said hydraulic expand cylinders,as shown in FIG. 13. (It is also possible to incorporate hydrauliccollapse cylinders to collapse the mandrels, instead of using returnsprings).

It should be noted that the outside diameter of the mandrel, formed bythe circle circumscribing the outer ends of the staves, remains circularand concentric throughout the expand/collapse range of the mandrel,unlike the prior art mandrel of FIG. 1 and all other known prior artmandrels, which are only circular at one diameter (usually the expandeddiameter).

Axial retention ring 34 is provided at the back to secure the mandrelassembly to the drive shaft 11 as shown in FIGS. 7 and 9. Said axialretention ring is bolted to the back end plate 18 a by cap screws 31which clamp the assembly on to shoulder 27 on said drive shaft.

Oil feed ring 19 is provided at the front, attached to front end plate18 by cap screws 31 and incorporates oil holes 23 and 24, to feedhydraulic oil from the axial hole 26 in the drive shaft, via radialholes 25 in the drive shaft, to the hydraulic cylinders (2) in end plate18. O-ring seals 32 seal the oil as it passes from the shaft into oilfeed ring 19, and o-rings 36 seal the oil as it passes from oil feedring 19 to front end plate 18. Axial hole 26 ends in a port at one endof shaft 11, the port being located at the end of said shaft from whichsaid hole was drilled, either at front or back of said shaft andhydraulic oil is supplied to this port using a commercial rotatingcoupling of prior art form.

At the back of the mandrel drive shaft 11 incorporates shoulder 27, towhich the back end plate is secured using axial retention ring 34,bolted to back end plate 18 a by screws 31 as described above. Thehydraulic oil is delivered to the back cylinders (2) via axial hole 26,radial holes 37 (2) and axial holes 38 which connect within back endplate 18 a to the hydraulic cylinders similarly to the connection at thefront, O-ring seal 36 in this case sealing the hydraulic oil as itpasses from the shaft directly to end plate 18 a. It should be notedhere that the back end plate 18 a is essentially similar to front endplate 18, but is to the opposite hand, since its internal hydraulicexpand cylinder pistons 21 must rotate the cage in the same direction asthe corresponding pistons in end plate 18, when viewed from the front ofthe mill, which is the opposite direction when viewed from the back ofthe mandrel.

As shown in FIGS. 7 and 9, drive shaft 11 and inner sleeve 12 are keyedtogether using axial keys 16 and 17, these keys being a press fit in thekeyways in shaft 11 and a slip fit in inner sleeve 12. A clearance slot40 is machined in the inner sleeve bore joining the keyways at each endto clear the keys at assembly. The keys 16 and 17 also pass throughkeyways 35 in end plates 18 a and 18. These keyways are extra wide andserve to limit the rotation of inner sleeve 12 and shaft 11 relative toend plates 18 and 18 a and cages 13 as the mandrel is expanded andcollapsed. This avoids the possibility of damage to the staves if theyjam into the end faces of the wedges (if the mandrel is collapsed toomuch) or slide off the top of the wedges (if the mandrel is expanded toomuch). As shown in FIG. 8 the side clearances between keys 16, 17 andkeyways 35 limit the rotation to plus and minus five degrees, or a totalof ten degrees between fully collapsed and fully expanded conditions.

Normally, as shown in FIG. 11, when expanding the mandrel, the stroke ofexpand piston 21 will be limited by the staves stalling against the boreof spool 106. However, if the spool bore is too large, or if the mandrelis expanded without a spool in place, keyways 35 provide a very usefulfunction in limiting the expansion stroke, as described above.

Quick Change and Pre-assembly

It can be seen from FIG. 7 that, if the outboard bearing support 52 isretracted, then it's possible to remove the mandrel assembly from shaft11 by releasing cap screws 31 at the back and sliding said mandrelassembly (except for axial retention ring 34) towards the front end andoff said shaft. If a spare mandrel assembly is available, it can be slidfrom the front end onto shaft 11 and secured in place by replacing capscrews 31 at the back end. This enables quick change of mandrels. Thestructure also lends itself to pre-assembly, using a dummy shaft (whichcould be a length of steel pipe mounted with axis horizontal mounted ona welded steel stand) in the maintenance shop. After pre-assembly of allcomponents, except axial retention ring 34 and back cap screws 31, on tothe dummy shaft, the assembly will be ready for quick installation atthe mill.

In FIG. 2 the remainder of the coiler assembly is shown. At the back endof the mandrel the drive shaft 11 extends back through and is supportedby two bearings 54 and 55 mounted in fixed pedestals 56 and 57respectively. The rotating portion 60 of a torque meter is keyed to theback end of shaft 11, and a coupling 58, keyed to the back end of saidrotating portion 60 of said torque meter and to the shaft of electricmotor 59, couples the said drive shaft to said motor.

In FIGS. 4, 5 and 8 and 11-13 the wedges 33 incorporated in inner sleeve12 are shown with the classic linear form, for the sake of simplicity.This is not the preferred form, as FIG. 5 illustrates. FIG. 5 shows twoviews of top stave 14, a wedge 33 and parts of cage 13, which can becompared with the corresponding view of these parts in FIG. 4. In theleft view, the inner sleeve and wedge have been rotated clockwiserelative to cage and stave in order to collapse the mandrel fully. Thisrotation causes the effective angle of the wedge to drop from 10 degreesto 4.26 degrees (rotation angle=10−4.26=5.74 degrees). In the rightview, the inner sleeve and wedge have been rotated counter-clockwiserelative to cage and stave in order to expand the mandrel fully, andthis rotation causes the effective angle of the wedge to increase from10 degrees to 15.30 degrees (rotation angle=15.30−10=5.30 degrees).Since the bottom surface of the stave is machined at the 10 degreeangle, full area contact between wedge and stave will only be achievedat the mid-stroke position as shown in FIG. 4. In this situation itwould be advisable to machine a convex crown on the inner end face ofthe staves to avoid point contact. Even so, only partial contact wouldbe achieved so stress in the contact area between wedge and stave wouldbe high, and wear on these parts would be high and uneven.

Furthermore, the ability of the mandrel to grip the spool would dependupon the inside diameter of spool 106. If said inside diameter was suchthat the staves gripped the spool at mid-stroke, the effective angle ofthe wedge would be 10 degrees. However, if said inside diameter werelarger, such that the staves gripped the spool close to the end of theexpansion stroke, the effective wedge angle would be close to themaximum of 15.3 degrees. This would not be conducive to obtaining atight grip between mandrel staves and the spool, because this angle istoo high.

The preferred form of the wedge surfaces is shown in FIG. 14. Thisfigure is a transverse section of the mandrel, showing cage 13, staves14, inner sleeve 12 and wedges 33. In this figure the topmost stave andits mating wedge is examined as before. Although the nominal wedge angleis set to 10 degrees as before, the wedge surface is made cylindricaland convex in form, the cylindrical profile having its center located onthe diameter line normal to the radius at the centerline of the stave,as shown. The inner (bottom) surface of the top stave 14 is machinedwith a matching concave cylindrical surface, this profile also havingits center in the same location as the center of the wedge profile. Inthis case, as the inner sleeve is rotated relative to said cage and saidend plates to raise and lower the wedge profile (and hence expand andcollapse the mandrel), the motion of the wedge profile, if small, willbe close to a pure radial (vertical) motion. Since the motion of thestave is radial due to its constraint by the radial slot in cage 13,virtually 100% area contact between wedge and stave is achieved as theinner sleeve is rotated relative to said cage and said end plates. Ofcourse the top stave examined is typical of all 24 staves, which arearrayed around the mandrel as shown, with equal 15 degree spacing. Notethat said relative rotation is limited to plus and minus 5 degrees (10degrees total) by the clearance provided between keys 16, 17 and keyways35 in end plates, as shown in FIG. 8.

In fact, during the initial part of the expansion stroke, before theouter ends of the staves contact the bore of spool 106, there isnegligible pressure and therefore zero wear on stave and wedgecontacting surfaces, even if 100% contact is not achieved. For thisreason, the mandrel is designed so that, at the point where the staveouter ends contact the spool bore, the inner sleeve has rotated about50% of its expansion stroke as shown in FIG. 11. At this point, theradial forces will be the highest, both before and during winding of thecoil. This is the point at which the centers of curvature of each wedgeand mating stave lie exactly on the diameter line normal to the stavecenter line, as shown in FIG. 14. Therefore for small excursions ofrotation of inner sleeve and wedges about this point, the direction ofmotion of both wedge profile and stave is purely radial, and 100%contact between each wedge and its mating stave is maintained. Inservice such excursions will be tiny, and will be outwards in case ofoutward elastic deflection of spool when mandrel is expanded inside anempty spool and in case of radial wear of spool bore, and inwards incase of inward elastic deflection of spool when coil is fully wound.

It should also be noted here that, by using mating cylindrical surfaceson wedges and staves as described above, the effective wedge angleremains at 10 degrees throughout the working expand/collapse stroke, anddoes not vary as was the case with the linear wedge profile.

It should be further noted that the ten degree wedge profile angle thatwe have used in these embodiments was selected purely for the sake ofclarity. It's possible to use greater or smaller angles depending uponthe specific application. A larger angle gives a bigger radial expansionstroke for a given rotation stroke of the inner sleeve, but less radialforce on the spool bore, and therefore less ability for the staves togrip the spool bore when high strip tensions are used. A smaller anglegives less radial expansion stroke (and thus less radial clearancebetween spool and mandrel when mandrel is collapsed when mounting spoolor removing spool, and coil) but enables higher grip forces to begenerated between staves and spool bore.

To achieve high accuracy in tension control, the motor should bedesigned for minimum moment of inertia and can be either A.C. or D.C.type, but must be driven at variable speed in order to maintain thecorrect tension in the strip as the coil builds up (during winding) orgets smaller (during unwinding) and the torque regulation system must bevery fast acting. The motor bearings should be low friction type, eitherhydrostatic or ball or roller bearing type and should be sealed usinglabyrinths rather than rubbing seals. Similarly, drive shaft supportbearings 54 and 55 and outboard bearing 51 should be sealed usinglabyrinths to avoid friction drag losses.

It is possible to use either conventional strip tensiometers, whichmeasure strip tension by measuring the force on a deflector roll aroundthe strip passes as said strip travels between rolling mill and coiler,or to use a torque meter of the bearingless variety, such as the MRCT86000V series manufactured by the S. Himmelstein and Company of HoffmanEstates, Ill. to measure the torque applied by the drive motor to thecoiler mandrel, from which the strip tension can be calculated. This isshown in FIG. 2. Said torque meter consists of shaft mounted portion 60and a stationary portion mounted underneath said shaft-mounted portion,and so hidden from view in FIG. 2.

Other devices such as an encoder mounted at the back of the drive motorto measure motor speed and to count the number of wraps on the coilwould be according to prior art.

What is claimed is:
 1. A coiler for coiling a thin metal strip on arolling mill, wherein said metal strip is coiled on a hollow cylindricalspool mounted on a collapsible mandrel, said mandrel being expanded togrip the inside diameter of said spool, and, in order to minimize thepolar moment of inertia of the rotary parts, said mandrel is directlycoupled to an electric motor, without intermediate gears or pulleys, andsaid mandrel expansion is achieved by synchronized radial movement of aplurality of at least eight support members, said support membersconsisting of metal rectangular staves slideably mounted in a hollowcylindrical cage having a plurality of axial slots equally spaced aroundthe circumference of said cage, and within each of said axial slots oneof said staves slides in a radial direction, each of said staves beingheld by return springs 15 in contact with one wedge of a set ofidentical wedges formed equally spaced on the outside of an innersleeve, said wedges being oriented in a circumferential direction, saidinner sleeve being mounted on and keyed to a cylindrical shaft, and, inorder to expand the mandrel, said inner sleeve and said shaft arerotated in one of a clockwise or a counter-clockwise direction aroundthe axis of the mandrel relative to said cage and said staves in orderto cause each of said staves to ride up a wedge, the motion of all saidstaves being synchronized by said equal spacing of said wedges and saidstaves, such that the outer ends of all of said staves always lie on atrue circle concentric with the mandrel axis, the diameter of saidcircle increasing, and thus said mandrel expanding as the staves ride upthe wedges, and, in order to collapse said mandrel, said inner sleeveand said shaft are rotated in the other of said clockwise orcounter-clockwise directions around the axis of the mandrel relative tosaid cage and said staves in order to cause each of said staves to downa wedge, the motion of all said staves being synchronized by said equalspacing of said wedges and said staves, such that the outer ends of allof said staves always lie on a true circle concentric with the mandrelaxis, the diameter decreasing and thus the mandrel collapsing, as thestaves ride down the wedges.
 2. A coiler mandrel according to claim 1wherein each wedge of said set of wedges is provided with a convexcylindrical surface, and each of said staves is provided with a matchingconcave cylindrical surface, whereby substantially full area contact isachieved between each of said wedges and its mating stave throughout theexpansion stroke of said mandrel.
 3. A coiler mandrel according to claim1 whereby the orientation of said wedges and said staves relative to thedirection of the strip tension torque is such that said tension torqueurges the staves and cage to rotate in a direction relative to saidinner sleeve and said shaft causing the staves to ride up the wedges andthus self tighten the wedges against the inside diameter of the spool.4. A coiler mandrel according to claim 1 wherein the inner sleeve andcage are axially located upon said cylindrical shaft by a front endplate, attached to the front end of said cage and a back end plate,attached to the back end of said cage, said end plates being mounted onand keyed to said cylindrical shaft and wherein the keyways 35 in saidend plates are much wider than the mating keys 16,17 in said cylindricalshaft, the sides of the keyways functioning as stops to limit therotation of said end plates and cage relative to said cylindrical shaft.5. A coiler mandrel according to claim 4 wherein said end plates eachincorporate at least two hydraulic expand cylinders 22, and said innersleeves incorporate at least two lugs 20 at each end, the piston 21 ofeach of said hydraulic expand cylinders bearing against the side of alug, so that pressurizing said hydraulic expand cylinders causesrotation of said inner sleeve and cylindrical shaft relative to said endplate said cage and said staves, causing said staves to ride up saidwedges thus expanding the mandrel.
 6. A coiler mandrel according toclaim 5 wherein return springs 29 and plungers 39 are incorporated insaid end plates to retract the pistons of said hydraulic expandcylinders, when pressure is released from said hydraulic expandcylinders in order to force said staves to ride down the wedges and thuscollapse the mandrel.
 7. A coiler mandrel according to claim 4 where anaxial retention ring 34 is provided at the back end of the mandrel, saidaxial retention ring engaging with a shoulder on said cylindrical shaft,and being attached to the back end plate 18 a by cap screws 31, retainsthe mandrel assembly on said cylindrical shaft, such that removal ofsaid cap screws enables said mandrel assembly less said axial retentionring and said cap screws to be removed from said cylindrical shaft, bysliding said mandrel assembly forward off the front end of saidcylindrical shaft.
 8. A coiler mandrel according to claim 4 where an oilfeed ring is provided at the front end of the mandrel, said oil feedring being bolted to the front end plate and said oil feed ringincorporating holes and seals enabling hydraulic oil to flow from acentral axial hole in said cylindrical shaft to said hydraulic expandcylinders in said front end of plate.
 9. A coiler mandrel according toclaim 4 where oil holes are provided in said cylindrical shaft and saidfront and back end plates enabling hydraulic oil to be delivered to allof said hydraulic expand cylinders from a single port on the axis ofsaid cylindrical shaft, this port being located either at the front endor the back end of said cylindrical shaft.
 10. A coiler mandrelaccording to claim 5 where hydraulic collapse cylinders are incorporatedin said end plates whose pistons each bear against the opposite side ofeach lug 20 from the side bearing against each hydraulic expand cylinderpiston 21, whereby releasing the pressure from said hydraulic expandcylinders and applying pressure to said hydraulic collapse cylinderscauses rotation of said end plates and said cage and stave assemblyrelative to inner ring and cylindrical shaft, causing said staves toride down said wedges, thus collapsing the mandrel, and, at the sametime, forcing the pistons in said hydraulic expand cylinders to retract,it being clear that, to enable the mandrels subsequently to be expandedby applying pressure to said hydraulic expand cylinders, the pressure inthe hydraulic collapse cylinders must first be released.